This proposal seeks to develop a functional architecture of prefrontal cortex. Everyday actions take place in a fluid context in which we must process complex stimuli to achieve multiple goals. The term executive control has been used to account for the various processes required for such flexible behavior and includes the ability to maintain and manipulate information in working memory, establish and monitor internal goals, select task-relevant information, and organize a plan of action to accomplish these goals. The aim of this proposal is to characterize these operations at a psychological level and identify their neural correlates, focusing on the contributions of prefrontal cortex. Neuroimaging and behavioral studies will be conducted with neurologically impaired and healthy populations to address these questions. The first series of studies will use a variety of stimulus materials to systematically explore the role of prefrontal cortex in maintaining and manipulating the contents of working memory. These experiments will contrast different hypotheses concerning the functional organization of prefrontal cortex, determining if the appropriate characterization is best described in terms of processing requirements, processing content, or a hybrid of these two components. In the second and third sections, these ideas will be applied in the study of the neural mechanisms involved in response selection and goal selection. The final section focuses on how information is maintained in working memory, testing specific hypotheses related to inhibitory control. Although inhibitory control plays a predominant role in many conceptualizations of prefrontal function, especially in how it interacts with and facilitates working memory, our knowledge of the neural correlates of this cognitive operation remains limited. Within each of the four sections, various stimulus materials will be used to test the generality of the functions under investigation as well as identify material specific components of the prefrontal network. Taken together, the studies will provide a rich database for assessing, the role of sub regions of prefrontal cortex in various aspects of complex, goal oriented behavior.